Origin: Medial head: posterior humerus
Insertion: Olecranon process of ulna
Artery: Profunda brachii
Nerve: Radial nerve
Action: Extends forearm
Antagonist: Biceps brachii muscle
The medial head arises from the posterior surface of the body of the humerus, below the groove for the radial nerve; it is narrow and pointed above, and extends from the insertion of the Teres major to within 2.5 cm. of the trochlea: it also arises from the medial border of the humerus and from the back of the whole length of the medial intermuscular septum. Some of the fibers are directed downward to the olecranon, while others converge to the tendon of insertion.